This invention relates to moldable materials prepared by blending thermoplastic compositions to obtain multiple component blends which have a combination of advantageous characteristics. The conversion of plastics utilizes machinery adapted to fabricate the plastic at temperatures within a range which is significantly narrower than the range of softening points of the polymeric resins which scientists have produced.
Polyphenylene oxide is an example of a polymer having a softening point which is sufficiently high that it is not practical to employ some conventional equipment for modling articles of polyphenylene oxide. However, polyphenylene oxide has been a component in blends which can be molded at temperatures of interest to some fabricators.
Polystyrene is among the less costly of commercially used resins, but some types of polystyrene have softening points which are low enough to limit the utility of the resin. Various proposals have been made for blends comprising polyphenylene oxide and polystyrene.
Lauchlan, et al, U.S. Pat. No. 3,660,531 describes the preparation of a resin blend containing polystyrene and significant amounts of an elastomer for imparting impact resistance and containing polyphenylene oxide to impart a higher moldingtemperature.
Cizek, U.S. Pat. No. 3,383,435 describes blends comprising styrene resin and polyphenylene ether.
Fox, U.S. Pat. No. 3,356,761 disperses powdered polyphenylene oxide in styrene or slightly modified styrene and polymerizes the composition to provide a moldable composition.
Gowan, U.S. Pat. No. 3,373,226 prepares films from a blend of polystyrene and polyphenylene oxide.
Most attempts to mix pellets of different molding compositions are unsatisfactory because of the general incompatibility of polymeric materials. When a mixture of molding pellets is extruded, there is generally a very weak extrudate by reason of the fracture lines at the boundaries amongst the different compositions. The discovery of a compatible blend of plastics, sometimes referred to as "plastic alloys", is a significant and unexpected discovery by reason of the incompatibility of most of the conceivable permutations of mixtures of plastics.
Notwithstanding the persistent effort to prepare appropriate blends, there has been a failure by others to prepare blends meeting some of the combinations of desired properties which are attained by the present invention.